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CION Cancer Clinics
APC mutation: which cancers, and how much risk | CION Cancer Clinics
An inherited APC fault mainly raises the risk of bowel cancer, and in classic FAP that risk is very high without regular checks. The same fault also raises the risk in the duodenum and thyroid, and rarely in the liver, stomach, pancreas and brain. This page explains each risk, when it appears across a lifetime, and why most of it can be managed. At CION Cancer Clinics, our oncologists explain what a gene result means for you and your family, and plan the checks that follow.
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Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed September 2026, next review due September 2027
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On this page
- Which cancers does an inherited APC fault cause?
- Where in the body does an APC fault raise risk?
- How does the risk change as a carrier gets older?
- The words doctors use, in plain language
- Does the risk differ between classic and attenuated FAP?
- What this page cannot tell you
- Four things families tell us, and what is actually true
- Common questions about APC and cancer risk
The short answer
Which cancers does an inherited APC fault cause?
An inherited APC fault mainly raises the risk of bowel cancer. Left unwatched, a person with classic FAP will almost certainly develop it, usually at a young age. The same fault also raises the risk of cancer in the duodenum, the thyroid and, rarely, the liver, stomach, pancreas and brain.
Why the bowel comes first
APC is the gene that keeps cells in the bowel lining from growing out of turn. With one copy broken from birth, the lining starts to form polyps, often in the teenage years. Each polyp is a small growth that can turn into cancer over time. When there are hundreds of them, one turning is close to certain.
Why this is a risk you can act on
The bowel risk is the one that can be managed best. Regular colonoscopy finds polyps while they are harmless, and planned bowel surgery removes most of the risk before cancer starts. Many carriers live full lives because the risk was found early.
The risks that remain after bowel surgery
Surgery on the bowel does not remove the risks elsewhere. The upper gut, the thyroid and a type of growth called a desmoid tumour still need attention for life.
A raised risk is not a diagnosis. It is a reason to be watched.Organ by organ
Where in the body does an APC fault raise risk?
The risks are not equal. The bowel dominates, and the rest range from important to rare.
Large bowel
The main risk by a wide margin. In classic FAP the bowel fills with hundreds or thousands of polyps. Without surgery, cancer usually develops by middle age, and often much earlier.
Usually managed by
- Colonoscopy from the teenage years
- Planned preventive bowel surgery
Duodenum and stomach
Polyps also grow in the first part of the small bowel, just after the stomach. Cancer here is less common than in the large bowel, but it becomes the main cancer risk once the bowel is removed. Stomach polyps are frequent and mostly harmless.
Thyroid
A small raised risk of thyroid cancer, seen mostly in young women. It is usually slow-growing and found by a neck ultrasound or a careful examination of the neck.
The rarer risks
These are uncommon, but doctors keep them in mind.
- A liver tumour in babies and toddlers
- A brain tumour, in a small number of families
- Pancreatic cancer, rarely
- Desmoid tumours, which are not cancer but can press on organs
Not sure whether this applies to you?
Ask an oncologistAcross a lifetime
How does the risk change as a carrier gets older?
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Early childhood
A rare liver tumour called hepatoblastoma can occur in very young children. Some specialists offer liver checks in the first years of life for children known to carry the family fault.
-
The teenage years
Bowel polyps usually begin to appear. This is why colonoscopy for carriers in classic FAP families starts in adolescence, well before anyone would normally think of it.
-
Early adulthood
Polyp numbers climb. This is usually when preventive bowel surgery is planned, timed around studies, work and marriage where the polyps allow it.
-
After bowel surgery
Attention moves to the duodenum, the remaining rectum or pouch, the thyroid and desmoid tumours. Upper gut scopes become the main regular check.
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Later adult life
Duodenal polyps tend to grow and multiply with age. Regular scopes continue, and the gap between them depends on what each one finds.
On your report
The words doctors use, in plain language
- Adenoma
- The type of bowel polyp that can turn into cancer if left in place. FAP polyps are adenomas.
- Classic FAP
- The full form of the condition, with hundreds or thousands of bowel polyps starting young.
- Attenuated FAP
- A milder form with fewer polyps appearing later. The bowel cancer risk is still well above normal.
- Duodenal polyps
- Polyps in the first part of the small bowel. They are checked with a scope passed through the mouth.
- Desmoid tumour
- A firm growth of fibrous tissue, often in the tummy wall or gut lining. It does not spread, but it can press on nearby organs.
- Penetrance
- How often a fault leads to disease among everyone who carries it. For classic FAP and the bowel, it is very high.
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Side by side
Does the risk differ between classic and attenuated FAP?
Classic FAP
Attenuated FAP
Hundreds to thousands of bowel polyps
Usually a few dozen polyps, sometimes fewer
Polyps from the teenage years
Polyps appear later, often in adult life
Bowel cancer almost certain without surgery
Bowel cancer risk high, but lower and later
Surgery is usually needed
Polyps can sometimes be removed by colonoscopy alone
Duodenal and thyroid checks for life
Duodenal checks still advised
Being straight with you
What this page cannot tell you
It cannot give you a personal risk figure. Where the fault sits inside the APC gene changes how many polyps grow, how early they come and whether desmoid tumours are likely. Two families with different APC faults can have very different courses. What your specific variant means is a question for the counsellor who ordered the test.
It cannot read a tumour report
Most ordinary bowel cancers carry an APC change inside the tumour. That is a somatic change, meaning it arose in the tumour only, and it is not inherited. Tumour testing is handled by our targeted therapy team. This page is about the inherited kind, present in every cell from birth.
Who this does not apply to
Most people with a bowel polyp or two do not have FAP. Polyps are common in older adults and are usually a one-off finding. The APC I1307K variant, found mostly in Ashkenazi Jewish families, carries only a small extra risk and does not cause FAP. If your report names that variant, this page overstates your risk.
Commonly believed
Four things families tell us, and what is actually true
"Once the bowel is removed, the APC risk is over."
The bowel risk falls sharply, but the fault is still in every cell. Duodenal polyps, thyroid changes and desmoid tumours still need regular checks. Stopping follow-up after surgery is one of the commonest avoidable mistakes.
"We have no bowel cancer in the family, so it cannot be FAP."
Around one in four people with FAP have no family history at all, because the fault arose new in them. A child with many polyps may be the first person in the family to carry it.
"Children are too young to worry about."
In FAP families, polyps can start in the early teens, and a rare liver tumour can occur in toddlers. This is one of the few inherited conditions where testing children is usually advised.
"Having polyps means cancer is already there."
Polyps are growths that could become cancer, not cancer itself. Most are harmless when found. Watching and removing them is exactly how the cancer risk is kept down.
Questions we are asked
Common questions about APC and cancer risk
Is bowel cancer certain if I carry an APC fault?
In classic FAP, bowel cancer is almost certain if the bowel is left unwatched. With regular colonoscopy and well-timed surgery, that risk falls to a small fraction of what it was. In attenuated FAP, the risk is lower and comes later, but it is still well above normal.
What is the second biggest risk after the bowel?
For most carriers it is the duodenum, the first part of the small bowel. Polyps there grow slowly with age and a few can turn into cancer. This is why an upper gut scope is part of lifelong follow-up, even after bowel surgery.
Are women at higher risk of thyroid cancer with APC?
Yes. The thyroid cancer linked to FAP is seen far more often in young women than in men. It is usually slow-growing. Many specialists suggest a neck ultrasound as part of regular checks, and your team will say how often.
Does an APC fault cause breast or ovarian cancer?
No. APC is not linked to breast or ovarian cancer in any meaningful way. If breast or ovarian cancer runs in the same family, that points to a different cause, and your counsellor may suggest a wider panel test to look for it.
Are desmoid tumours a type of cancer?
No. They do not spread to other organs. But they can grow into nearby tissue and press on the gut or blood vessels, so they are taken seriously. They are more likely after abdominal surgery in some APC families, which affects how surgery is planned.
If my APC result is attenuated, can I skip colonoscopy?
No. A milder form still carries a bowel cancer risk well above the general population. The checks may start later and some people can manage with colonoscopy alone, without surgery. The plan is set by your specialist from what each scope finds.
Does diet or lifestyle change the APC risk?
Not in any way that replaces checks. A healthy diet, not smoking and staying active are good for everyone, but they do not stop polyps forming in FAP. Some medicines to slow polyp growth have been studied, and the evidence so far is limited.
Who should I talk to about my own risk?
A genetic counsellor or clinical geneticist, together with a gastroenterologist who sees polyposis. Bring your report and any colonoscopy results. Call the CION helpline if you are unsure where to start, and counselling in Telugu can be arranged.
Your Specialists
Meet CION's oncologists. Bring your family history or genetic report to them.
Our medical oncologists see people with a strong family history of cancer, arrange genetic counselling and testing where it fits, and plan the checks that follow.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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Sources
- GeneReviews (NCBI) — APC-Associated Polyposis Conditions
- MedlinePlus Genetics — Familial adenomatous polyposis
- MedlinePlus Genetics — APC gene
- National Cancer Institute — Genetics of Colorectal Cancer (PDQ)
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
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